Field of the Invention
The invention is in the field of food safety technologies. In particular, it relates to a method for inactivating Cronobacter sakazakii. 
Description of the Related Art
Cronobacter spp. (formerly known as Enterobacter sakazakii) is an gram-negative, motile, non-spore forming, rod-shaped and facultative anaerobe foodborne pathogen, which can survive at 6° C.˜45° C. and grow well at 37° C.˜43° C. A few of Cronobacter strains can grow slowly above 47° C. or below 0° C. Cronobacter can grow in many kinds of culture medium, such as nutrient agar, eosin methylene blue (EMB) agar, tryptone soy agar (TSA) and deoxycholate agar, etc. All of Cronobacter strains can rapidly grow on TSA and deoxycholate agar, forming bacterial colonies with a diameter of 1˜1.5 mm after cultivation at 36° C. for 24 hours and forming bacterial colonies with a diameter of 2˜3 mm and producing yellow pigment after cultivation at 36° C. for 48 hours. Cronobacter has strong acid resistance and weak alkaline resistance.
At present, Cronobacter spp. has been included in the list of foodborne pathogens, which can be isolated from a wide range of food materials (e.g. meat, cheese, vegetables, grains, herbs, spices and powdered infant formula), environment (e.g. factories and homes) and insects. The CDC testing report between 2010 and 2011 showed that the Cronobacter detection rate of 175 food samples from Wuzhou, Guangxi was 5.26%, the Cronobacter detection rate of 891 food samples from Suqian, Jiangsu was 2.6%, the Cronobacter detection rate of 286 food samples from Changsha, Hunan was 6.3%. The data above suggested that the contamination of Cronobacter spp. in food was widely distributed in China.
Research has shown that the sources of Cronobacter spp. contamination are mainly from three areas. The first source comes from clinical hospitals. In 1980, Farmer et al. first detected Cronobacter from patient's body fluid and secretion, and Cronobacter were found in the respiratory tracts of 29 patients in the same hospital 7 months later. The second source is from powdered infant formula. Although there are a lot of living places for Cronobacter in the environment, Cronobacter in powdered infant formula is directly related to human diseases. Lversen et al. detected Cronobacter and Enterobacteriaceae from powdered infant formula and 402 other food materials. The results showed that the detection rate in formula food, dried infant food, milk powder and cheese food were 2.4%, 10.2%, 4.1% and 3.3%, respectively. Other enteric bacteria and Salmonella were not detected in these foods. The third source is from the natural environment. Cronobacter spp. is widely distributed in the environment. Cronobacter was isolated from soil, sewer, plant roots and animal excrement as early as 1974. Therefore, in order to prevent contamination of Cronobacter, not only strict monitoring of the food production process is necessary, but strict disinfection of food production environment is also needed.
Cronobacter spp. in PIF (powdered infant formula) is classified as a Class A pathogen. The Cronobacter contamination in PIF can cause neonatal infection in new born babies and lead to serious diseases, such as bacteremia, necrotizing enterocolitis and cephalomeningitis, which have a death rate as high as 40% to 80%. China is a big PIF production and consumption country. We have been facing the problem of Cronobacter contamination that has long time plagued the PIF industry.
Powdered infant formula is a main source of Cronobacter spp. contamination and transmission. There are two major ways for Cronobacter contamination and transmission. The first way of contamination occurs during the process of raw materials addition and product drying and packaging in PIF production. The second way is contamination of PIF production environment, usage of contaminated equipments or during the process of milk powder reconstitution. Cronobacter has strong environmental tolerance, which enables it to survive in final products and the PIF processing environment.
Although PIF is a major source of Cronobacter contamination and transmission, it still can be safe to eat as long as its production, processing and consumption are handled properly. Research showed that the PIF treated with high temperature or low temperature can reduce the survival rate of Cronobacter. In addition, some food additives can reduce the strains' temperature tolerance, and may directly kill the bacteria. For the production equipment, especially the inner wall of each pipeline which is easy to form biofilms, timely cleaning and effective disinfection are necessary to reduce the risk of Cronobacter contamination. For milk powder reconstitution, cleaning and disinfecting the tableware in advance are needed. The temperature of water needs to be higher than 80° C. It's better not to eat the leftover of the dissolved milk to avoid the second contamination of Cronobacter. To reduce the risk of Cronobacter contamination, continuous monitoring of raw materials and production environment must be carried out. To completely prevent and control Cronobacter, there is a urgent need of a safe and effective method for inactivating Cronobacter. 
In recent years, natural extracts have attracted the attention of researchers because of their natural advantage, convenience and easy access. The antimicrobial effect of natural extracts has also attracted much attention. The use of natural extracts to prevent and control Cronobacter contamination becomes the future trend of development.